Rollers for use in printing and method of making same

ABSTRACT

Transfer or cleaning roller for use in offset printing is flocked with fibers adhesively secured to the roller by a layer of elastic binder. The outer ends of the fibers project from the layer of binder but are coated therewith, with the possible exception of their tips, which may be free of binder in the case of transfer rollers.

SUMMARY OF THE INVENTION

This invention relates to improvements in the rollers used in printing,and especially in offset printing, for moistening and inking purposes,etc.

It is conventional for these various purposes to provide a roller, forexample, a rubber roller or one made of a flexible plastic material,with a cover of cloth or leather. Such rollers are, for example, used inthe offset process to insure the moistening of the plate before it isinked, and it is the present practice to use a knitted tubular sleeve ofseamless construction. It is difficult to thread such a sleeve on thesupport because the sleeve must grip the support very tightly. Moreover,these sleeves have the disadvantage, especially when they are new, thatthey tend to shed. The particles shed by the sleeve are deposited on theplate and cause defects in the printed impression.

It has been suggested that these knitted tubular sleeves be replaced byvelvet coverings, sewn or adhesively secured to the support, which areless subject to shedding. The common disadvantage of these two types ofcoverings is that they have a seam which leaves traces on certain typesof work, in particular, flat work.

It has also been proposed that sleeves be used which contract when theycome in contact with water, which facilitates their mounting on thesupport. These, however, require supports of special hardness. Moreover,they are thin, and for this reason retain an inadequate supply of liquidand dry rapidly whenever the machine is stopped. Moreover, they are veryfragile when dry and quite expensive.

All these coverings, with the exception of adhesively secured coverings,have the additional disadvantage of twisting about the support if thetension thereon is insufficient. They are, in general, difficult to washbecause the moisteners pick up ink during the operation and this inkpenetrates into the fibers of the cloth or knitted material.

For inking during offset printing, it has also been suggested that aroller be used which is covered with teaseled leather. These rollershave good absorptive qualities with respect to the ink and make itpossible to eliminate many of the defects in printing such as specks orflecks which are caused by particles shed by the moisteners, or powdersor particles of paper, or particles of ink. These rollers covered withleather have, however, various disadvantages. In the first place, it isnecessary to use a different roller for each color of ink because theleather absorbs the ink and cannot be completely cleaned. Moreover, theyhave a seam along their entire length and the leather must be frequentlyrestretched. The leather must also be frequently teaseled to preserveits properties.

It has also been suggested that the surface of a printing roller becovered with textile fibers deposited by flocking. These rollers havenot been practical because they had certain disadvantages. In the firstplace, the fibers came unstuck easily when subjected to substantialfriction during use. Moreover, the fibers lay tangentially whichconsiderably reduced the supply of water contained by these rollers whenused for moistening purposes.

The present invention is designed to improve the properties of printingrollers the surface of which is covered by textile fibers deposited byflocking in order to permit their use in the printing field withoutsuffering from the disadvantages of known rollers. One object of thepresent invention is to permit the inexpensive manufacture of amoistening roller adapted to deposit a film of water on a plate-carryingcylinder.

It is also an object of the present invention to provide aparticle-collecting roller which is inexpensive and reliable inoperation so as to collect practically all of the particles from aplate-carrying cylinder with which the roller cooperates.

Finally, it is an object of the invention to provide a processpermitting the easy and inexpensive manufacture of a printing rollerhaving improved properties.

The roller according to the invention has on its surface textile fibersdeposited by flocking and is characterized by the fact that the textilefibers are connected to each other by an elastic binder surrounding thefibers over at least a substantial part of their length.

The use of a binder makes it possible to consolidate the attachment ofthe fibers to their support to form a relatively rigid assembly whichhas a certain porosity. Moreover, when used as an inking roller, thefibers are not in contact with the ink.

The fibers used may be natural, artificial or synthetic fibers. For amoistening roller, rayon is preferred, and for a particle collectingroller, nylon is preferred.

The particle collecting roller according to the invention has individualfibers the fineness of which lies between 4 and 20 deniers and a fiberlength of 0.5 - 3 mm.

A representative particle collecting roller may advantageously be madefrom nylon fibers having a fineness of 6 deniers and 1 mm long.

For a moistening roller, the fineness of the fibers is between 4 and 20deniers and the length of the fibers is between 1 and 3 mm. For such aroller, a rayon fiber is preferably of the order of 5 deniers and about1.5 mm long.

The elasticity of the binder, when solidified, is that of a rubberhaving, in the pure state, a Shore hardness of between 25 and 90 andpreferably between 55 and 70.

The binder may be a solution of rubber or a polyurethane base binder, apolyvinyl chloride, or any other elastic binder. Preferably the flockingadhesive may have the same chemical structure as the binder.

The construction of the particle collecting roller is characterized bythe fact that the fibers, in at least most cases, are entirely coveredby the binder and that between the fibers or groups of fibers connectedtogether are free spaces extending over a substantial portion of thelength of the fiber. Thus the roller has, from its surface outward, athin layer of flocking adhesive, for example between 10/100 and 2/10thof a mm. thick, and a thicker layer of binder, for example, one third ofthe total length of the fibers, with the fibers projecting from saidlayer but being themselves covered with binder. The structure of themoistening roller is distinguished from that of the particle collectingroller solely by the fact that the layer of binder is much thinner, sothat a much longer flexible portion of the fibers, which is also coveredby the binder, extends from the layer. In a particularly advantageousmanner the ends of the fibers of this moistening roller may have nobinder so that these fibers can absorb moisture.

The process according to the invention comprises the steps of depositingon a cylinder, for example, a metallic cylinder covered with a flexiblelayer of rubber, polyvinyl chloride, or another elastomer, a thin layerof flocking adhesive, flocking the roller with textile fibers,preferably by an electrostatic flocking process, drying the adhesive,removing the excess of fibers deposited on the cylinder, and thencoating the flocked cylinder with at least one layer of elastic binder.

In order to produce the particle collecting roller, the cylinder mayadvantageously be rotated about a horizontal axis after the applicationof the binder during drying of the binder.

In an advantageous method of making a moistening roller, a less viscousbinder is used than in the case of a particle-collecting roller. Afterapplication of the binder, the moistening roller is preferablypositioned vertically and the positions of its ends reversed after acertain time. When the binder is dry, the tips of the fibers arecleaned, for example, by mounting the roller on a turntable and treatingits surface with an abrasive cloth.

The layer of flocking adhesive is applied with a brush or spray gun.Preferably the layer of binder is applied with a brush.

The support on which the fibers are mounted may be metallic orsynthetic. In particular, it is possible to provide an intermediatetextile layer between the support and the fibers. The surface of theroller may be smooth.

The porous and spongy nature of the roller according to the inventionenables it to absorb a large supply of liquid. The structure issufficiently rigid to resist the forces applied thereto during use andthe textile fibers, even though they project, are anchored sufficientlywell to prevent their being torn off by friction.

Other advantages and characteristics of the invention will appear from areading of the following description of a preferred embodiment thereof,given purely by way of illustration and example, with reference to theaccompanying drawings, in which:

FIG. 1 is a schematic view in axial section on an enlarged scale of aparticle-collecting roller.

FIG. 2 is a schematic view, partially in axial section, on an enlargedscale, of a moistening roller.

1. Manufacture of a Particle-Collecting Roller

A metallic cylinder is used, for example, one made of a steelconventionally used in the manufacture of particle-collecting rollers,said roller being covered in a known manner with a thick sleeve ofrubber or an elastomer. A thin layer of an elastic flocking adhesvie issprayed thereon. This adhesive is very viscous having a viscosity of30 - 100 centipoises and preferably 45 to 85 centipoises according tothe LVT Brookfield test, 30t/mn, rotor No. 2/25° C. Such an adhesivemay, for example, be the adhesive sold under the designation UK 1430 bythe Henkel company of Germany.

Immediately after the application of this layer, the roller iselectrostatically flocked with 6 denier nylon fibers 1 millimeter longuntil a surplus of fibers has been applied. The adhesive is thenpermitted to dry or drying is facilitated by heating. After drying, thesurplus fibers are removed by brushing. The fibers are then coated byapplying the binder UK 1430 above specified, having the same viscosity,with a brush. This coating with a brush has the effect of creating anexcess of binder.

After coating, the roller is mounted on a horizontal axis and rotatedslowly until the binder is dry. During this rotation the excess binderis eliminated. After drying of the binder, the roller is ready for use.

It is remarkable to observe that a roller made in this manner will pickup practically all the particles appearing on a plate-carrying cylinder,the most resistant particles being removed upon completion of the thirdturn of the cylinder, whereas known rollers will not pick up more than60 to 70% of these particles.

2. Manufacture of a Moistening Roller

In the same way as already described, 5 denier rayon fibers of 1.5 mm inlength are flocked. After drying of the adhesive and removal of theexcess fibers, the roller is coated with the same binder as before, butin a more dilute state, for example, in a solution containing 1/3 ofbinder per 2/3 of a solvent, such as toluene.

After coating with an excess of binder, the roller is positionedvertically and the excess is permitted to run off. After a certainamount of time, the roller is positioned vertically on its other enduntil drying of the binder has been completed.

Once the binder has been dried, the roller is mounted on a turntable androtated while applying thereto an abrasive cloth so as to remove part ofthe binder which covers the free end of the flocked fibers.

As a variation, when using a binder such as rubber for example, thebinder may advantageously be diluted with benzene when used to coat themoistening roller.

FIG. 1 shows the rubber sleeve 1 coaxial with the shaft 1a. The innermetallic cylinder is not shown. On the sleeve 1 is located a thin layerof adhesive 2 into which the bases of the nylon fibers 3 penetrate. Itwill be seen that the nylon fibers are covered with binder 4 whichforms, above the layer 2, a layer having a thickness 5, for example ofthe order of 1/3 of the total length of the fibers 3. It will be seenthat the fibers are entirely covered by the binder 4 but that there arespaces or cells 6 between the fibers which may receive the particles tobe collected.

Referring now more particularly to FIG. 2, this shows the rayon fibers 7positioned in the adhesive 2 and a layer of binder 8 which is thinnerthan the layer 5. It will also be seen that the tips 9 of the fibers arefree of binder, and a textile layer 10 is provided between the sleeve 1and the adhesive 2.

What is claimed is:
 1. Printing roller comprising a support, a firstthin adhesive layer on said support flocked with textile fibers havingone end adhesively secured to and embedded in said first layer andprojecting radially therefrom, a second layer of elastic binder appliedon said first layer and connecting said fibers to each other, thethickness of said second layer being greater than that of said firstlayer, and said fibers projecting outwardly beyond said second layer. 2.Printing roller as claimed in claim 1 wherein the part of each fiberwhich extends outward from said second layer has a coating of saidelastic binder, the coatings on adjacent fibers being discrete from eachother over at least most of their length.
 3. Roller as claimed in claim1, in which the textile fibers have a length between 0.5 and 3 mm and afineness between 4 and 20 deniers.
 4. Roller as claimed in claim 1, inwhich said binder is selected from the group consisting of rubber,polyvinyl chloride and polyurethane.
 5. Roller as claimed in claim 1, inwhich the Shore hardness of the pure binder lies between 25 and
 90. 6.Roller as claimed in claim 1, in which the binder is of the samematerial as the flocking adhesive.
 7. Roller as claimed in claim 1, inwhich the viscosity of the adhesive lies between 30 and 100 centipoises.8. Roller as claimed in claim 1, in which the binder incompletely coversthe fibers, which have a free end uncovered by binder.
 9. Roller asclaimed in claim 1, in which the surface of the roller is straight. 10.Roller as claimed in claim 1, in which said support is metallic. 11.Roller as claimed in claim 1, in which said support has a base made of amaterial having the elasticity of rubber.
 12. Roller as claimed in claim1, comprising a textile layer interposed between the support and theflocked fibers.